HBM is a Space Saver

HBM is such an exciting technology, but how does it work? Well, think of a GPU and many squares around it - these are the GDDR5 chips - but with HBM, the DRAM can be placed right next to the GPU chip itself, saving a considerable amount of space on the PCB.

This image above shows you just how much space will be saved with a HBM stack, with a 1GB chip of GDDR5 taking up 672mm2 of space, while the same 1GB HBM will take up just 35mm2 of space - saving a huge 1900% space. Incredible, isn't it?

We also have 9900mm2 PCB footprint for the Hawaii XT-based Radeon R9 290X which uses GDDR5, but for an HBM-based ASIC, we're looking at less than 4900mm2, which is more than 50% smaller. So, just in PCB space alone, we're saving a considerable amount of physical space.

Increased Speeds & Improved Power Efficiency with HBM

Now that we can see just how much PCB space can be saved by using HBM, which is paramount, what type of performance improvements can we expect over GDDR5? Well, a considerable improvement, that's what.

As you can see from the slide above, GDDR5 has a 32-bit wide memory bus per package, while providing up to 1750MHz (7Gbps). HBM cranks things up by magnitudes, with 1024-bit wide memory bus with up to 500MHz (1Gbps). With four chips of DRAM used, the 1024-bit bus is multiplied by four up to 4096-bit, which is what the Radeon R9 390X is expected to pack.

GDDR5 has 28GB/sec of bandwidth per chip, while HBM really starts to stretch its legs in its first generation with over 100GB/sec per stack. As for power consumption, GDDR5 uses 1.5V and HBM uses 1.3V.

Whilst GDDR5 has just 10.66GB/sec of bandwidth per watt of power used, HBM has over 35GB/sec of bandwidth per watt. This means the HBM and interposer provide many times more bandwidth than GDDR5, all while using over 50% less power. AMD says that "HBM rebalances DRAM vs. logic power consumption to protect future GPU performance growth".

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